The development of high energy battery systems requires the compatibility of an electrolyte possessing desirable electrochemical properties with highly active anode materials, such as lithium, calcium, sodium and the like, and the efficient use of high energy density cathode materials, such as fluorinated carbon, copper sulfide and the like. The use of aqueous electrolytes is precluded in these systems since the anode materials are sufficiently active to react with water chemically. It has, therefore, been necessary, in order to realize the high energy density obtainable through use of these highly reactive anodes and high energy density cathodes, to turn to the investigation of nonaqueous electrolyte systems and more particularly to nonaqueous organic electrolyte systems.
The term "nonaqueous organic electrolyte" in the prior art refers to an electrolyte which is composed of a solute, for example, a salt or complex salt of Group I-A, Group II-A or Group III-A elements of the Periodic Table, dissolved in an appropriate nonaqueous organic solvent. Conventional solvents include propylene carbonate, ethylene carbonate or .gamma.-butyrolactone, or the like. The term "Periodic Table" as used herein refers to the Periodic Table of the Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 48th Edition, The Chemical Rubber Co., Cleveland, Ohio, 1967-1968.
A multitude of solvents is known and recommended for use but the selection of a suitable solvent has been particularly troublesome since many of the solvents which can be used to prepare electrolytes sufficiently conductive to permit effective ion migration through the solution are reactive with the highly reactive anodes described above. Consequently, many investigators in search of suitable solvents have concentrated on aliphatic and aromatic nitrogen- and oxygen-containing compounds with some attention given to organic sulfur-, phosphorus- and arsenic-containing compounds. The results of this search have not been entirely satisfactory since many of the solvents investigated still could not be used effectively with extremely high energy density cathode materials, such as fluorinated carbon, and were sufficiently corrosive to lithium anodes to prevent efficient performance over any length of time.
U.S. Pat. No. 3,547,703 to Blomgren et al discloses the use of a nonaqueous battery electrolyte employing a solute dissolved in ethylene glycol sulfite. U.S. Pat. Nos. 3,536,532 and 3,700,502 disclose nonaqueous cells employing solid fluorinated carbon [(CF.sub.x).sub.n ] as the active cathode material in conjunction with a light metal anode and a conventional nonaqueous electrolyte.
French Pat. No. 2,124,388 discloses a nonaqueous electrolyte using dioxolane as the solvent.
U.S. application Ser. No. 509,820 now U.S. Pat. No. 3,907,597 by G. W. Mellors discloses a nonaqueous electrolyte comprising sulfolane or its liquid alkyl-substituted derivatives in combination with a low viscosity cosolvent and an ionizable solute. Another U.S. application Ser. No. 462,792 now U.S. Pat. No. 3,871,916 by M. L. Kronenberg discloses a nonaqueous electrolyte based on 3-methyl-2-oxazolidone in combination with a low viscosity solvent and an ionizable solute.
U.S. Pat. No. 3,567,515 to Maricle et al discloses a nonaqueous cell system wherein sulfur dioxide is employed to form what is referred to as a "passivating" film on a highly active metal, such as lithium, said film being some form of metal-sulfur dioxide complex or reaction product which prevents substantial further attack of sulfur dioxide on the metal. In a similar manner, an article titled "Kinetics of the Solid Lithium Electrode in Propylene Carbonate" appearing in the J. Electrochemical Society, Vol. 117, No. 3, Mar. 1970, discloses that propylene carbonate may form a film on lithium metal through the reaction between the lithium and the propylene carbonate.
A Final Report dated Sept., 1967 under a Contract No. DA-28- 043-AMC-02304 (E) USAECOM discloses the use of propylene carbonate as a good solvent for use in nonaqueous cells along with the listing of many other possible solvents. Crotonitrile is listed as a possible solvent; however, it was found that when it was in contact with lithium, the rate of corrosion of lithium was excessive. Therefore, crotonitrile was not pursued as a solvent having comparable properties to propylene carbonate.
It is thus known in the art that while the theoretical energy, i.e., the electrical energy potentially available from a selected anode-cathode couple, is relatively easy to calculate, there is a need to choose a nonaqueous electrolyte for such couple that permits the actual energy produced by an assembled battery to approach the theoretical energy. The problem usually encountered is that it is practically impossible to predict in advance how well, if at all, a nonaqueous electrolyte will function with a selected couple. Thus a cell must be considered as a unit having three parts, a cathode, an anode and an electrolyte, and it is to be understood that the parts of one cell are not predictably interchangeable with parts of another cell to produce an efficient and workable cell.
It is an object of the present invention to provide a nonaqueous cell employing among other components a liquid organic electrolyte consisting essentially of crotonitrile in combination with a protective cosolvent and a solute.
It is a further object of the present invention to provide a nonaqueous cell which utilizes a highly active metal anode, such as lithium, a solid cathode such as (CF.sub.x).sub.n, copper sulfide, copper oxide, nickel fluoride or silver chloride, and a liquid organic electrolyte comprising crotonitrile in combination with a protective cosolvent and a solute.
It is a further object of the invention to provide an electrolyte solvent system for nonaqueous solid cathode cells consisting essentially of crotonitrile in combination with a protective cosolvent, a low viscosity cosolvent and a solute.
It is a further object of this invention to provide a nonaqueous cell which utilizes a metal anode, a solid cathode and a liquid organic electrolyte based on crotonitrile in combination with a protective cosolvent such as propylene carbonate and a solute such as LiClO.sub.4.